The primary function of a roof structure is to protect a lower space below the roof structure from external elements such as wind and precipitation. A typical pitched roof structure includes a plurality of parallel load-bearing rafters that slope from a ridge at the top of the roof structure to an eave at a lowermost edge of the roof structure, and a plurality of parallel battens disposed on top of, and extending orthogonally with respect to, the rafters. A pitch angle of the roof structure is defined between the rafters and a horizontal plane that includes the eave.
Roof covering elements such as tiles are affixed along the battens in horizontally-extending rows or courses. Each course of tiles underlaps the course of tiles directly above and overlaps the course of tiles directly below, such that the tiles overlap in a ridge-to-eave direction. The tiles of the roof structure act as a primary drainage system. Precipitation that falls on the roof structure flows down the tiles towards the eave and into a gutter arranged beneath and parallel to the eave. The gutter then carries the precipitation away from the roof structure.
The tiles typically incorporate certain design features to prevent precipitation penetrating between the tiles. For example, within a course of tiles, the left-to-right neighbouring tiles may be arranged to interlock with one another to guard against water penetration between neighbouring tiles of a course. Between the courses, upper and lower neighbouring tiles may be provided with weather checks that guard against ingress of upwardly wind-driven rain. An example of such tiles is described in the Applicant's granted patent GB2454709, in which the weather checks are ridges disposed on the undersurface of a tile, that, in a tiled roof, rest on the upper surface of a tile in the course below. The weather checks guard against ingress of precipitation by increasing the tortuosity of the upward path of precipitation. This is particularly important in low-pitched roof structures, which term is understood in the art to mean roof structures having a pitch between approximately 10° and approximately 15°.
Roof structures often include additional roof components that are accommodated on or in, or that extend through, the roof structure. For example, components such as windows (known in the art as rooflights), vents, sun pipes, fire escapes or false chimneys may be incorporated. Such roof components require an aperture in the tiles of the roof structure, so as to allow light, air or the roof component to pass through the tiles.
When such components are incorporated into roof structures, it is important that measures are taken to guard against precipitation leaking into the space beneath the roof structure, for example via gaps between the roof component and the surrounding tiles. In particular, precipitation is prone to leak between the roof component and the course of tiles that extends directly below the roof component (referred to hereafter as the lower bordering course).
It is known, therefore, to provide flashing that supplements the primary drainage system of the tiles to resist penetration of precipitation. For example, the aperture may be encircled by a frame that is surrounded by flashing that extends from the frame a short distance up, down and across the roof to surround the frame. Above and to the sides of the aperture, the flashing lies above the battens and below the tiles. Beneath the aperture, a lower portion of the flashing extends downwardly and is raised over an uppermost edge of the lower bordering course, such that the flashing is brought onto an upper surface of the tiles of that course. The lower portion of the flashing therefore incorporates a distinct upward step that brings the lower portion from a position below the tiles to a position above the tiles.
In use, the flashing catches precipitation that falls between the aperture and the surrounding tiles. That precipitation flows downwardly from the area surrounding the aperture onto the lower portion of the flashing. As the precipitation flows down the lower portion, it is guided over the step at the uppermost edge of the lower bordering course, and hence is guided onto the upper surface of the tiles of that course. The precipitation then flows down the upper surface of those and subsequent lower tiles in the usual way.
There are significant disadvantages associated with such known flashing systems, which limit their effectiveness in preventing leakage of precipitation, especially in low-pitched roof structures.
Firstly, to raise the lower portion of the flashing over the lower bordering course, the lower portion must be brought between the tiles of the lower bordering course, and the overlapping tiles of the course above. In this way, the flashing lifts the upper course of tiles away from the tiles of the lower bordering course, firstly creating an undesirable gap between the courses and secondly disrupting contact between the weather check of the upper tile and the surface of the lower tile. The gap and the disruption to the weather checks allow ingress of upwardly wind-driven rain between the courses, resulting in leakage.
Secondly, at the sides of the aperture the flashing disrupts the tiles of the roof structure. The flashing covers the battens, so that the tiles cannot be fixed to the battens in the vicinity of the aperture; however the tiles must lie as close as possible to the aperture in the interest of preventing leakage. These conflicting requirements mean that tiles must be cut precisely to size so as to be fixed in place around the aperture, and there is little room for error. An improper job in cutting and laying the tiles, for example by a rushed or negligent tiler, frequently leads to problematic leakage around the aperture. Furthermore, if the tiles are profiled (i.e. having an undulating surface) the tiles may need to be cut at different points on the profile, leaving gaps of varying depth beneath the tiles, further hindering fixing and sealing of the tiles.
Such flashings are still more problematic when used in low-pitched roof structures. Where the flashing steps upwardly over the uppermost edge of the lower bordering course, a horizontal trough is defined in the flashing. Precipitation and debris can collect in the trough, preventing effective drainage. This problem can be mitigated to some extent by trimming the top edge of the tiles immediately below the rooflight to reduce the depth of the trough. However, this process is time consuming and detrimental to the function of the tile because it effectively reduces the overlap of the tiles, and it does not, in any case, avoid the problem altogether.